msm: mdss: check intr line status before handling isr

Hardware might return/call the pending interrupt
on one CPU when same interrupt is disabled from other
core. Such parallel processing may lead to unclocked
register access in interrupt context followed by
panic. It is safe to check the interrupt line status
before handling isr to avoid crash in such race
condition.

Change-Id: I460550cb5188c7f77b9f741682917010f9231a50
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>